The invention relates to a method for correcting a patterned film by focused ion beam etching of a sample such as a photomask, a reticle, an X-ray mask, or the like, in a semiconductor manufacturing process.
In the prior art as shown in FIG. 2(a), when removing an excess portion 2 of a patterned film from a substrate 4 by focused ion beam etching with a scanning focused ion beam 1, imaging of the patterned film at the periphery of the excess portion 2 on substrate 4 is performed by detecting secondary charged particles which are generated from the pattern or the substrate 4 by irradiation with the scanning focused ion beam 1. And then, only the excess portion 2 of the pattern film is repeatedly irradiated with the scanning focused ion beam 1 for removal of the excess portion, while monitoring secondary charged particles emitted from the excess portion 2 or from the substrate 4 adjacent the excess portion 2. By monitoring the secondary charged particles at each irradiation point, each end point of the removal process by the irradiation with the scanning focused ion beam can be detected.
In the conventional method as described the above, when the excess patterned film 2 is removed by irradiation with the focused ion beam 1, the amount of material removed is greater at the edges of the excess portion 2 than at the interior of the excess portion due to the edge effect. Further, the focused ion beam scatters at a small angle at the edges of the excess film portion 2, impinges on the substrate 4 at the periphery of the excess portion 2 and etches the substrate 4 at or adjacent the periphery of the excess portion 2. This constitutes unnecessary or harmful processing which creates a groove 5 at the periphery of the excess film portion 2, as shown in FIG. 2(b). When the sample is a photomask or a reticle to be used for the production of semiconductor device, there is a problem that this groove 5 scatters or refracts light which is recognized as a new defect of the sample.